Optical fiber connectors are a critical part of essentially all optical fiber communication systems. For instance, such connectors are used to join segments of fiber into longer lengths, to connect fiber to active devices, such as radiation sources, detectors and repeaters, and to connect fiber to passive devices, such as switches, multiplexers, and attenuators. The principal function of an optical fiber connector is to hold the fiber end such that the fiber's core is axially aligned with an optical pathway of the mating structure. This way, light from the fiber is optically coupled to the optical pathway.
Of particular interest herein are “expanded beam” optical connectors. Such connectors are used traditionally in high vibration and/or dirty environments, where “physical contact” between the fiber and the light path of mating connector is problematic. Specifically, in dirty environments, particulates may become trapped between connectors during mating. Such debris has a profoundly detrimental effect on the optical transmission since the particles are relatively large compared to the optical path (e.g., 10 microns diameter in single mode) and are therefore likely to block at least a portion of the optical transmission. Furthermore, in high-vibration environments, optical connectors having ferrules in physical contact tend to experience scratching at their interface. This scratching diminishes the finish of the fiber end face, thereby increasing reflective loss and scattering.
To avoid problems of debris and vibration, a connector has been developed which expands the optical beam and transmits it over an air gap between the connectors. By expanding the beam, its relative size increases with respect to the debris, making it less susceptible to interference. Further, transmitting the beam over an air gap eliminates component-to-component wear, thereby increasing the connector's endurance to vibration. Over the years, the expanded beam connector has evolved into a ruggedized multi-fiber connector comprising an outer housing which is configured to mate with the outer housing of a mating connector, typically through a screw connection. Contained within the outer housing are a number of inner assemblies or “inserts.” Each insert comprises an insert housing, a cable assembly contained within the insert housing, and a ball lens at a mating end of the insert housing optically connected to at least one fiber of the cable assembly. The ball lens serves to expand and collimate light at the connector interface. When two expanded beam connectors are mated, there is an air gap between the ball lenses of each pair of optically coupled inserts.
Tyco Electronics Corporation (Harrisburg, Pa.) currently offers a line of expanded beam connectors under the brand name PRO BEAM®. This connector and improvements thereto are described in U.S. Pat. No. 7,722,261, hereby incorporated by reference. The current design uses a 3.0 mm ball lens mounted on the front end of the insert cavity and affixed with epoxy. A cable assembly having a ferrule holding at least one fiber is produced separately, and is mounted into the insert with the ferrule optically coupled with the ball lens. In the single mode design, the ferrule brings the fiber endface in contact with the ball lens in order to achieve a high return loss.
Although the multimode (MM) and single mode (SM) expanded beam connectors offered by Tyco Electronics Corporation have consistently met industry requirements, applicants have identified a need for improved manufacturability. For example, the insert is machined with a radiused, annular ridge to seat the ball lens. This radiused seat must be machined with close tolerance (e.g. 2 μm) relative to the position of the ferrule tip. Not only is machining such a curved seat challenging, but also verifying its tolerance compliance is error prone. Thus, the existing verification process tends to be unreliable such that the tolerance compliance of the assembly is not known with any real certainty until the final optical measurement is performed on the product. Determining noncompliance at this stage of manufacture is inefficient and wasteful.
Additionally, during insertion of the cable assembly into the cavity, often the ferrule scrapes along the sidewall of the insert's borehole, creating shavings or debris. This debris may settle on the ferrule end face in a way that can degrade the signal and the return loss. Due to the presence of machining tolerances and the difficulty of verification, it is often required that tuning is applied in order to align the fiber axis of the cable assembly with the axis of the lens.
Therefore, there is a need to improve the manufacturability of the conventional expanded beam product. The present invention fulfills this need among others.